JP2005116045A - Optical head, and optical information recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that the total number of optical elements constituting an optical head is increased in many cases as an optical function such as the compensation of spherical aberration is added in a conventional optical head, therefore, aberration in the respective optical elements are overlapped, thereby increasing the aberration of a whole optical system. <P>SOLUTION: As astigmatic quantity of the spherical aberration compensation system becomes the minimum by arranging a first lens 5 and a second lens 6 constituting the spherical aberration compensation system so that the direction of astigmatism is straight, the aberration of the whole optical head system can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical pickup device used for optical information processing and an optical disk drive device having the optical pickup device.

  In an optical system of an optical pickup that records and reproduces information on an optical disk medium such as a DVD or Blu-ray disk, in order to increase the density of information recorded on the information storage medium, the numerical aperture NA of the condensing optical system is increased and the wavelength is increased. Have been proposed and put to practical use.

  However, as the numerical aperture NA increases, the spherical aberration generated by the thickness error of the base material that is the protective layer of the information storage medium increases. As means for correcting this, a method of generating a spherical wave with an objective lens and generating a spherical aberration with an objective lens has been devised and already put into practical use.

  FIG. 9 is a configuration diagram of an optical head in a conventional information recording / reproducing apparatus described in Patent Document 1. In FIG. The divergent light emitted from the light source 101 becomes parallel light by the collimator lens 102 and passes through the beam splitter 103. The beam that has passed through the beam splitter 103 passes through the spherical aberration correction means 106 and is focused on an information storage medium 108 such as an optical disk by an objective lens 107 driven by a first actuator 109.

  Here, the spherical aberration correcting means 106 is generated due to a spherical aberration caused by a thickness error of the protective layer of the information recording medium 108 or a difference in the thickness of the protective layer when recording / reproducing on the information storage medium having a multilayer structure. The spherical aberration is reduced by changing the distance between the first lens 104 and the second lens 105 using the second actuator 110.

The beam condensed by the objective lens 107 is reflected and diffracted by a track on the information storage medium 108. The reflected / diffracted beam again passes through the objective lens 107, is reflected by the beam splitter 103, and is collected by the detection lens 111. The condensed beam enters the light detection element 112, and a signal recorded in the information storage medium 108 is detected.
JP 2003-109219 A Principles of Optics: Max Born and Emil Wolf, PERGAMON PRESS (1975)

  However, in the conventional optical head, as the optical function such as the spherical aberration correction is added, the total number of optical elements constituting the optical head is often increased, and thus the optical head is configured. There is a problem that the aberrations of the optical elements to be overlapped with each other and the aberration of the entire optical system increases. Accordingly, it is necessary to improve the quality of the optical element in order to suppress the aberration of each optical element.

  In the optical head, a method of reducing coma and spherical aberration among the aberrations by adjusting the optical head is often used.

  Specifically, the coma aberration can be adjusted and reduced by adjusting the tilt of the objective lens, and the spherical aberration can be adjusted by adjusting the distance between the light source and the collimator lens to intentionally reduce the parallelism of the collimator lens. Can be reduced.

  However, the astigmatism of the entire optical head cannot be reduced by correction. However, with respect to the optical head of the system that shapes the light intensity distribution of the parallel light emitted from the collimator lens using a prism, only the astigmatism component orthogonal to the beam shaping direction is used between the collimator lens and the light source. Astigmatism can be corrected by adjusting the interval, but other astigmatism components cannot be corrected.

  The present invention solves the above-described problems, and provides an optical head with less astigmatism of the entire optical system of the optical head, and hence less aberration of the entire optical system. Further, by using the optical head, An optical information recording / reproducing apparatus having high stability and reliability during signal recording / reproducing is provided.

  In order to achieve the above-mentioned object, an invention according to claim 1 of the present invention is an optical head for recording or reproducing a signal on an information recording medium, comprising: a light source; and a recording surface protective layer of the information recording medium. Spherical aberration correction means for correcting spherical aberration generated when the thickness deviates from the standard value, an objective lens for condensing the light emitted from the light source on the information recording medium, and receiving reflected light from the information recording medium In addition, in the optical head provided with a photodetecting element that outputs a signal for reproducing the information recorded in the information storage medium, the spherical aberration correcting means includes a negative lens and a positive lens, and the positive lens and The negative lens is an optical head in which the directions of astigmatism of each lens are substantially orthogonal.

  As a result, for example, the amount of astigmatism of the entire spherical aberration correction unit can be minimized, and hence the aberration of the entire optical head optical system can be reduced. Can be improved.

  In order to achieve the above-mentioned object, the invention according to claim 2 of the present invention is an optical head for recording or reproducing a signal with respect to an information recording medium, comprising a light source and a recording surface protective layer of the information recording medium. Spherical aberration correction means for correcting spherical aberration generated when the thickness deviates from the standard value, an objective lens for condensing the light emitted from the light source on the information recording medium, and receiving reflected light from the information recording medium In addition, in the optical head provided with a photodetecting element that outputs a signal for reproducing the information recorded in the information storage medium, the spherical aberration correcting means includes a negative lens and a positive lens, and the positive lens and In the negative lens, the astigmatism directions of the respective lenses are substantially orthogonal, and further, the astigmatism direction of the positive lens or the negative lens and the beam shaping direction of the beam shaping optical element. There is a substantially equal optical head.

  As a result, for example, the amount of astigmatism of the entire spherical aberration correction unit can be minimized, and hence the aberration of the entire optical head optical system can be reduced. Can be improved. Further, since the amount of astigmatism in the beam shaping direction can be adjusted by adjusting the distance between the beam shaping optical element and the collimator lens, the amount of astigmatism of the entire spherical aberration correction means can be adjusted. Can be further reduced.

  In order to achieve the target, the invention according to claim 3 of the present invention is the optical head according to claim 1 or 2, wherein the spherical aberration correcting means further has a chromatic aberration correcting function.

  Thereby, for example, an optical head with little aberration fluctuation can be configured with respect to the wavelength fluctuation of the light source.

  The optical head according to any one of claims 1 to 3, wherein the positive lens is a lens group composed of two or more lenses in order to achieve the target. It is.

  Thereby, for example, in the positive lens, it is possible to configure an optical system with less aberration fluctuation with respect to the lens tilt.

  The optical head according to any one of claims 1 to 3, wherein the negative lens is a lens group composed of two or more lenses in order to achieve the target. It is.

  Thereby, for example, in the negative lens, it is possible to configure an optical system with little aberration fluctuation with respect to the lens tilt.

  According to a sixth aspect of the present invention, the positive lens and the negative lens are cemented lenses obtained by cementing two or more lenses made of glass materials having different Abbe numbers. Or it is an optical head of 5.

  Thereby, for example, an optical head with little aberration fluctuation can be configured with respect to the wavelength fluctuation of the light source.

  In order to achieve the above-mentioned object, according to a seventh aspect of the present invention, at least one of the lens surfaces of the positive lens or the lens constituting the negative lens is an aspherical surface. 8. The optical head according to any one of 7 above.

  Thereby, for example, among the positive lens and the negative lens, in the lens having the aspheric surface, it is possible to configure an optical system with less aberration fluctuation with respect to the lens tilt.

  In order to achieve the above-mentioned object, an invention according to claim 8 of the present invention is an optical head for recording or reproducing a signal on an information recording medium, wherein a light source and a light beam emitted from the light source are converted into a parallel light beam. A collimator lens for converting, an objective lens for condensing the parallel light flux on the information recording medium, and a signal for receiving reflected light from the information recording medium and reproducing the information recorded on the information recording medium. An optical head provided with an output light detection element, wherein the astigmatism direction of the collimator lens is substantially orthogonal to the astigmatism direction of the objective lens.

  As a result, for example, the amount of astigmatism generated by the combination of astigmatism of the objective lens and astigmatism of the collimator lens can be minimized, so that the aberration of the entire optical head optical system can be reduced. Since it can reduce, the condensing characteristic of the said objective lens can be improved.

  In order to achieve the above target, an invention according to claim 9 of the present invention is an optical head for recording or reproducing a signal on an information recording medium, wherein a light source and a light beam emitted from the light source are converted into a parallel light beam. A collimator lens for conversion, a beam shaping optical element for converting the light quantity distribution of the parallel light flux into a circle, an objective lens for condensing the parallel light flux on the information recording medium, and reflection from the information recording medium In an optical head comprising a light detecting element that receives light and outputs a signal for reproducing information recorded in the information storage medium, the direction of astigmatism of the collimator lens and non-reflection of the objective lens The direction of astigmatism is substantially orthogonal to the direction of astigmatism of the collimator lens or the direction of astigmatism of the objective lens, and the direction of astigmatism of the beam shaping optical element. The direction of the beam shaping is substantially equal optical head.

  As a result, for example, the amount of astigmatism generated by the combination of astigmatism of the objective lens and astigmatism of the collimator lens can be minimized, so that the aberration of the entire optical head optical system can be reduced. Since it can reduce, the condensing characteristic of the said objective lens can be improved. Further, by adjusting the distance between the beam shaping optical element and the collimator lens, the amount of astigmatism in the direction of the beam shaping can be adjusted, so by adjusting the amount of astigmatism of the entire optical head optical system, Further reduction can be achieved.

  In order to achieve the above-mentioned object, the invention according to claim 10 of the present invention is a cemented lens in which the positive collimator lens further has a chromatic aberration correction function, and two or more lenses made of glass materials having different Abbe numbers are cemented. The optical head according to claim 8 or 9, wherein

  Thereby, for example, an optical head with little aberration fluctuation can be configured with respect to the wavelength fluctuation of the light source.

  In order to achieve the above-described object, according to an eleventh aspect of the present invention, in the lens surface of the objective lens or the collimator lens, at least one surface is an aspherical surface. The optical head according to Item 1.

  Thereby, for example, in the constituent lens having the aspherical surface, it is possible to configure an optical system with less aberration fluctuation with respect to the lens tilt.

  In order to achieve the above object, an invention according to claim 12 of the present invention is an optical head for recording or reproducing a signal to or from an information recording medium, and includes a light source and light from the light source in the information recording medium. An objective lens that condenses light, a detection lens that converts return light reflected by the information storage medium into convergent light, and a signal that receives the convergent light and reproduces information recorded on the information storage medium. An optical head provided with an output light detecting element, wherein the astigmatism direction of the objective lens and the astigmatism direction of the detection lens are substantially orthogonal.

  Thereby, for example, the magnitude of astigmatism of the convergent light collected by the detection lens can be reduced, and information recorded on the information storage medium detected by the light detection element is reproduced. Signal quality can be improved.

  In order to achieve the target, the invention according to claim 13 of the present invention is characterized in that the beam shaping optical element is a prism, or any one of claims 2 to 7, or 9 to 11. The optical head.

  Thereby, for example, the elliptical light intensity distribution in the light emitted from the light source can be converted into a circular shape, and the shape of the focused spot by the objective lens can be reduced.

  In order to achieve the goal, according to claim 14 of the present invention, the beam shaping optical element is a lens, or any one of claims 2 to 7 or claim 9 to claim 11. The optical head.

  Thereby, for example, the elliptical light intensity distribution in the light emitted from the light source can be converted into a circular shape, and the shape of the focused spot by the objective lens can be reduced.

  In order to achieve the above-mentioned object, the invention according to claim 15 of the present invention is the astigmatism of each positive lens and negative lens constituting the spherical aberration correcting means passing through the respective lens central axes. The optical head according to any one of claims 1 to 7, wherein a mark indicating the direction of astigmatism is applied to an intersection of a straight line directed in the direction of the lens and each lens outer peripheral portion.

  Thereby, for example, the astigmatism direction of the positive lens and the negative lens can be easily identified, and the arrangement of the positive lens and the negative lens becomes easy.

  In order to achieve the above-mentioned goal, in the invention according to claim 16 of the present invention, the positive lens and the negative lens are held in a lens barrel, pass through the center axis of each lens, and reduce the astigmatism of each lens. 8. The optical head according to claim 1, wherein a mark indicating the direction of astigmatism is applied to an intersection of a straight line directed in the direction and the lens barrel holding each lens. 9.

  Thereby, for example, the astigmatism direction of the positive lens and the negative lens can be easily identified, and the arrangement of the positive lens and the negative lens becomes easy.

  In order to achieve the target, the invention according to claim 17 of the present invention is based on an intersection of a straight line passing through the central axis of the objective lens toward the astigmatism of the objective lens and the outer periphery of the objective lens. The optical head according to any one of claims 8 to 14, wherein a mark indicating a direction of astigmatism is applied.

  Thereby, for example, the direction of astigmatism of the objective lens can be easily identified, and the arrangement of the objective lens is facilitated.

  In order to achieve the target, the objective lens according to claim 18 of the present invention is such that the objective lens is held in a lens barrel, passes through the central axis of the objective lens, and travels in the direction of astigmatism of the objective lens. The optical head according to any one of claims 8 to 14, wherein a mark indicating the direction of astigmatism is applied to an intersection between a straight line and the lens barrel holding the objective lens.

  Thereby, for example, the direction of astigmatism of the objective lens can be easily identified, and the arrangement of the objective lens is facilitated.

  In order to achieve the target, the invention according to claim 19 of the present invention is based on an intersection of a straight line passing through the central axis of the collimator lens and in the direction of astigmatism of the collimator lens and the outer periphery of the collimator lens. The optical head according to any one of claims 8 to 11, wherein a mark indicating a direction of astigmatism is applied.

  Thereby, for example, the direction of astigmatism of the collimator lens can be easily identified, and the arrangement of the collimator lens is facilitated.

  In order to achieve the target, in the invention according to claim 20 of the present invention, the collimator lens is held in a lens barrel, passes through the central axis of the collimator lens, and goes in the direction of astigmatism of the collimator lens. The optical head according to any one of claims 8 to 11, wherein a mark indicating the direction of astigmatism is applied to an intersection between a straight line and the lens barrel on which the collimator lens is held.

  Thereby, for example, the direction of astigmatism of the collimator lens can be easily identified, and the arrangement of the collimator lens is facilitated.

  In order to achieve the target, the invention according to claim 21 of the present invention is the intersection of a straight line passing through the central axis of the detection lens and directed to the direction of astigmatism of the detection lens and the outer periphery of the detection lens. 13. The optical head according to claim 12, wherein a mark indicating the direction of astigmatism is applied.

  Thereby, for example, the direction of astigmatism of the detection lens can be easily identified, and the arrangement of the detection lens is facilitated.

  In order to achieve the above-mentioned goal, according to a twenty-second aspect of the present invention, the detection lens is held by a lens barrel, passes through the central axis of the detection lens, and moves toward the astigmatism of the detection lens. 13. The optical head according to claim 12, wherein a mark indicating the direction of astigmatism is applied to an intersection between a straight line and the lens barrel on which the detection lens is held.

  Thereby, for example, the direction of astigmatism of the detection lens can be easily identified, and the arrangement of the detection lens is facilitated.

  In order to achieve the target, the invention according to claim 23 of the present invention is the optical head according to any one of claims 1 to 22, wherein the NA of the objective lens is 0.7 or more.

  Thereby, for example, an optical head capable of recording / reproducing a high-density information recording medium can be configured.

  24. The optical head according to any one of claims 1 to 23, wherein the wavelength of the light source is 380 nm to 420 nm in order to achieve the target.

  Thereby, for example, an optical head capable of recording / reproducing a high-density information recording medium can be configured.

  In order to achieve the above-mentioned object, an invention according to claim 25 of the present invention is an optical information recording / reproducing apparatus for recording or reproducing a signal on an information recording medium, and recording or reproducing a signal on the information recording medium. 25. An optical information recording / reproducing apparatus which is an optical head according to any one of claims 1 to 24.

  Thereby, for example, information can be recorded / reproduced on / from the information recording medium with an optical head having good condensing characteristics, so that an optical information recording / reproducing apparatus with high stability and reliability during signal recording / reproduction can be configured.

  As described above, according to the present invention, at least one of a positive lens and a negative lens, an objective lens and a collimator lens, or an objective lens and a detection lens constituting the spherical aberration correcting means constituting the optical head. In this lens, the amount of astigmatism due to the combination of the at least one set of lenses can be minimized by making the directions of astigmatism of the respective lenses substantially orthogonal, and thus the entire optical head optical system. The aberration can be reduced.

  In addition, since the optical head according to the present embodiment is used as an optical head, information can be recorded on and reproduced from an information recording medium with an optical head having good condensing characteristics, and stability and reliability during signal recording and reproduction can be improved. A high optical information recording / reproducing apparatus can be constructed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
In Embodiment 1, an example of the optical head of the present invention will be described.

  FIG. 1 is a configuration diagram of an optical head according to the first embodiment.

  In FIG. 1, 2 is a light source, 3 is a collimator lens, 4 is a beam splitter, 5 is a first lens, 6 is a second lens, and the first lens 5 and the second lens 6 are used to record an information recording medium. 8 forms a spherical aberration correction system for correcting spherical aberration caused by the deviation of the base material thickness of the protective layer 8 from the standard value. Further, 7 is an objective lens, 9 is a detection lens, and 10 is a light detection element.

  Here, the light source 2 is constituted by, for example, a semiconductor laser element, and is a light source that outputs coherent light for recording and reproduction to the recording layer of the information recording medium 8. The collimator lens 3 is a lens that converts divergent light emitted from the light source 2 into parallel light. The beam splitter 4 transmits the light that has passed through the collimator lens 3 to the objective lens 7 side, and reflects the reflected light from the information recording medium 8 to the light detection element 10 side.

  The objective lens 7 is a lens that collects light on the recording layer of the information recording medium 8. The detection lens 9 is a lens that condenses the light reflected by the information recording medium 8 on the light detection element 10. The light detection element 10 receives light and converts the light into an electrical signal.

  The operation of the optical head configured as described above will be described with reference to FIG. The light emitted from the light source 2 is collimated by the collimator lens 3. The light that has passed through the collimator lens 3 passes through the beam splitter 4, passes through the first lens 5 and the second lens 6 that constitute the spherical aberration correction system, and then passes through the information by the objective lens 7. The light is condensed on the recording medium 8.

  Next, the light reflected from the information recording medium 8 passes through the objective lens 7, passes through the spherical aberration correction system, is reflected by the beam splitter 4, and is reflected by the detection lens 9 to the light detection element 10. It is focused on. The light detection element 10 outputs a focus error signal indicating the focused state of light on the information recording medium 8 according to the condensed light, and outputs a tracking error signal indicating the light irradiation position. Here, the focus error signal and the tracking error signal are detected by a known technique, for example, by the astigmatism method and the push-pull method.

  A focus control means (not shown) controls the position of the objective lens 7 in the optical axis direction so that light is always focused on the information recording medium 8 in a focused state based on a focus error signal. A tracking control means (not shown) controls the position of the objective lens 7 based on the tracking error signal so that light is condensed on a desired track on the information recording medium 8. Information recorded on the information recording medium 8 is also obtained from the light detection element 10.

  Next, the present invention will be described in detail. First, the direction of astigmatism is defined using FIG. In the lens 1 of FIG. 2, a two-dimensional orthogonal coordinate system xy is defined on the lens surface as shown. Here, the origin (x, y) = (0, 0) of the x-axis and y-axis is the rotation center of the lens surface. Now, the lens 1 is often rotationally symmetric with respect to the central axis, and since aberrations are normally discussed within a circle within the effective diameter, polar coordinates (r, θ) are also defined as shown in FIG. Therefore, (x, y) = (r cos θ, r sin θ).

As a method of mathematically handling an arbitrary function expressed in the polar coordinate system, a method of developing with orthogonal components by a Zernike polynomial is often used. In wave optics, wavefront aberration is the phase distribution of light in the polar coordinates, and it is known that each orthogonal component of the phase distribution of light developed by the Zernike polynomial represents various components of wavefront aberration. Yes. Details are described in Reference 1 and will be omitted, but here, among the components obtained by expanding the phase distribution of the light passing through the lens surface with the Zernike polynomial in the polar coordinate system, the 0,90 degree component of astigmatism _Note that the phase distribution (AS _0,90 ) referred to as is represented by Equation 1 and the phase distribution (AS _{± 45} ) referred to as the ± 45 degree component of astigmatism is represented by Equation 2. Here, A and B are the sizes of the respective components.

Here, the 0,90 degree component of astigmatism is
The direction of θ = 0 degrees, that is, the x-axis direction of FIG.
2 is an astigmatism component in which the difference in focal length from the direction of θ = 90 degrees, that is, the y-axis direction in FIG. Define. The same applies to the ± 45 degree component of astigmatism, and the direction obtained by rotating the x axis or the y axis by 45 degrees is defined as the direction of the ± 45 degree component of astigmatism.

  The addition of (Equation 1) and (Equation 2) results in the phase distribution of astigmatism in the polar coordinate system, and when these sums are expressed using only sin, (Equation 3) is obtained.

  Accordingly, from Equations 1 to 3, in the coordinate system of FIG. 2, the astigmatism has a magnitude A of 0, 90 degrees component of the astigmatism X component and a magnitude of ± 45 degrees component of the astigmatism. In the present specification, the vector will be referred to as an astigmatism vector. Furthermore, the astigmatism vector direction φ is defined as the astigmatism direction, and the vector size C is defined as the astigmatism magnitude.

Now, in FIG. 1, the astigmatism of the spherical aberration correction system constituted by the first lens 5 and the second lens 6 will be considered. Astigmatism phase distribution of the first lens 5 when the angle formed by the astigmatism vectors of the first lens 5 and the second lens 6 with respect to the first lens 5 is ψ. Is expressed by Equation 4, and the phase distribution of astigmatism of the second lens 6 is expressed using (Equation 5). Here, C ₁ and C ₂ (≧ 0) are the magnitudes of astigmatism.

  The phase distribution of astigmatism in the spherical aberration correction system is expressed by the synthesis of (Equation 4) and (Equation 5), and in (Equation), sin2θ = −sin (2θ + ψ), that is, ψ = 90. Or ψ = 270 degrees, that is, if the first lens 5 and the second lens 6 are arranged so that the directions of astigmatism are orthogonal, the entire spherical aberration correction system Astigmatism can be minimized, and in this case, the absolute value of the magnitude of astigmatism in the spherical aberration correction system is (Equation 6).

By arranging each lens so that the astigmatism directions of the first lens 5 and the second lens 6 are orthogonal, the astigmatism of the spherical aberration correction system is minimized, and the spherical aberration is further reduced. Astigmatism of the entire correction system is smaller than the astigmatism of the first lens 5 and the second lens 6 alone. If the above arrangement is not performed, astigmatism having a maximum size of C ₁ + C ₂ occurs at ψ = 0 ° or ψ = 180 °, and the wavefront aberration of the optical system increases.

In the equations (4) and (5), when C ₁ = 0.03λ and C ₂ = 0.03λ, the astigmatism of the spherical aberration correction system, the first lens 5 and the second lens 6 FIG. 3 shows an example in which the relationship with the angle ψ formed by each astigmatism vector is specifically calculated.

  When the astigmatism vectors of the first lens 5 and the second lens 6 are parallel, the astigmatism of the spherical aberration correction system is maximized, and when the astigmatism vectors are orthogonal, The astigmatism of the spherical aberration correction system becomes zero.

  For the aberration of the optical system, an index called Marshall's evaluation criterion is generally used, and according to the index, when collimated light is favorably condensed to the diffraction limit by a lens, the wavefront aberration of the parallel light is 0.07λ. The following is considered desirable.

  In FIG. 3, in the case of the conventional method, the astigmatism of the spherical aberration correction system may occur at a maximum of 0.06λ, which significantly deteriorates the wavefront aberration of the optical head. The astigmatism of the spherical aberration correction system is 0.02λ or less even when the angles formed by the astigmatism vectors of the lens 5 and the second lens 6 are substantially orthogonal, for example, within a range of 90 ± 20 degrees. The wavefront aberration can be greatly improved.

  In FIG. 1, the first lens 5 and the second lens 6 constituting the spherical aberration correction system are arranged so that the direction of astigmatism is orthogonal. Therefore, the amount of astigmatism in the spherical aberration correction system is minimized. In this case, if a mark indicating the direction of astigmatism is provided in advance in the direction of astigmatism of each lens, the direction of astigmatism can be easily understood at the time of assembling the lens, and assembly becomes easy. For example, in FIG. 1, the direction of astigmatism of the first lens 5 is the direction from the center of the first lens 5 toward the second mark 12, and the direction of astigmatism of the second lens 6. Is a direction from the center of the second lens toward the third mark 13.

  For high-density recording, the objective lens may have a large numerical aperture, for example, 0.7 or more, and a short wavelength light source, for example, a light source having a wavelength of about 380 nm to 420 nm may be used as the light source of the optical head. The first lens 5, or the second lens 6, or the first lens 5 and the second lens 6 are combined with a plurality of spherical or aspherical lenses using glass materials having different Abbe numbers. If a combination lens is used and is configured as a color correction lens, even if the numerical aperture of the objective lens is large, it is possible to suppress the occurrence of aberration of the optical head due to wavelength fluctuations of the light source. As the number of components increases, the astigmatism of each lens overlaps and the aberration increases. In particular, when an aspherical lens is used as a constituent lens, an aspherical lens created by the press method often has a large astigmatism compared to a spherical lens generally produced by polishing. Also in this case, astigmatism can be reduced by arranging the astigmatism directions of the lens group corresponding to the first lens 5 and the lens group corresponding to the second lens 6 to be orthogonal to each other. It becomes.

  As described above, in FIG. 1, by arranging the respective lenses so that the astigmatism directions of the first lens 5 and the second lens 6 constituting the spherical aberration correction system are orthogonal, FIG. Thus, the aberration of the optical head can be suppressed to a small level, and the light condensing characteristics of the objective lens 7 of the optical head can be improved.

(Embodiment 2)
In Embodiment 2, an example of the optical head of the present invention will be described.

  FIG. 4 is a configuration diagram of the optical head of the second embodiment. Since the optical head in FIG. 4 is the same as that described in the first embodiment, a duplicate description is omitted. The head shown in FIG. 4 is different from the head shown in Embodiment 1 in that a beam shaping optical element 4 ′ is used as the beam splitter 4. When a semiconductor laser light source is used as the light source 1 in FIG. 4, the emitted light of the semiconductor laser light source often has an elliptical intensity distribution. The emitted light having the emitted elliptical intensity distribution is converted into parallel light by the collimator lens 3, and the minor axis direction of the elliptical intensity distribution is enlarged by the beam shaping optical element 4 ′, or the major axis By reducing the direction, the parallel light is converted into parallel light having a circular intensity distribution.

  As the beam shaping optical element 4 ', for example, a prism or a lens including a surface having a different curvature radius with respect to a certain orthogonal direction can be used.

  In this case, if the parallelism of the parallel light is slightly deviated, the beam shaping optical element is caused by the difference in the beam magnification in the x4 direction and the y4 direction shown in FIG. 4 of the beam shaping optical element 4 ′ in FIG. Astigmatism occurs in the beam shaping direction in the 4 ′ outgoing light. In other words, the amount of astigmatism can be adjusted by slightly moving the collimator lens 3 and breaking the parallelism of the emitted light in the beam shaping direction.

  In the first embodiment, in FIG. 4, the respective lenses are arranged so that the astigmatism directions of the first lens 5 and the second lens 6 constituting the spherical aberration correction system are orthogonal. As a result, the amount of astigmatism in the spherical aberration correction system can be reduced, but cannot be completely reduced to zero, and a residual of | C1−C2 | is generated. However, astigmatism can be canceled by fine adjustment of the collimator lens if the astigmatism directions of the first lens 5 and the second lens 6 coincide with the beam shaping direction. Accordingly, it is possible to suppress the aberration of the optical head in FIG. 4 to be small, and it is possible to further improve the condensing characteristics of the objective lens of the optical head.

(Embodiment 3)
In the third embodiment, an example of the optical head of the present invention will be described.

  FIG. 5 is a configuration diagram of an optical head according to the third embodiment. The optical head of FIG. 5 is the same as that described in the first embodiment, and a duplicate description is omitted. In the head of FIG. 5, for example, the objective lens 7 is an aspherical lens composed of a single lens or a plurality of lenses, and the first lens 5 and the second lens 6 constituting the spherical aberration correcting means are a single spherical surface. The polishing lens and the collimator lens 3 are assumed to be composed of an aspheric lens composed of a single lens or a plurality of lenses.

  Aspherical lenses are often manufactured using glass or resin pressing methods, resin molding methods, etc., and spherical lenses are often manufactured using polishing methods, and the pressing method uses molding conditions to suppress astigmatism compared to the polishing method. Astigmatism may occur due to lens assembly adjustment errors even when the lens is composed of a plurality of lenses. Therefore, in FIG. 5, since the spherical aberration correcting means is composed of a spherical polishing lens, there is little astigmatism, and the astigmatism difference between the objective lens 7 and the collimator lens 3 is dominant in the optical head. . Therefore, if the respective lenses are arranged so that the astigmatism directions of the objective lens 7 and the collimator lens 3 are orthogonal, the aberration of the optical head can be suppressed, and the objective lens of the optical head can be suppressed. It is possible to improve the light condensing characteristics.

  Also in this case, if a mark indicating the direction of astigmatism is provided in advance in the direction of astigmatism of each of the objective lens 7 and the collimator lens 3, the direction of astigmatism can be easily achieved when the lens is assembled. Easy to understand and assemble. For example, in FIG. 5, the astigmatism direction of the objective lens 7 is the direction from the center of the objective lens 7 toward the fourth mark 14, and the astigmatism direction of the collimator lens 3 is the collimator lens 3. The direction from the center to the first mark 11.

(Embodiment 4)
In Embodiment 4, an example of the optical head of the present invention will be described.

  FIG. 6 is a configuration diagram of an optical head according to the fourth embodiment. The optical head in FIG. 6 is the same as that described in the first embodiment, the second embodiment, and the third embodiment, and a duplicate description is omitted. In the head shown in FIG. 6, a beam shaping optical element 4 ′ is used as the beam splitter 4 as in the second embodiment. Further, in the fourth embodiment, as in the third embodiment, for example, the objective lens 7 is an aspherical lens composed of a single lens or a plurality of lenses, the first lens 5 constituting the spherical aberration correcting means, and The second lens 6 is composed of a single spherical polishing lens, and the collimator lens 3 is composed of an aspherical lens composed of a single lens or a plurality of lenses. Since the spherical aberration correcting means is composed of a spherical polishing lens, there is little astigmatism, and the astigmatism difference between the objective lens 7 and the collimator lens 3 is dominant in the optical head. Therefore, the respective lenses are arranged so that the astigmatism directions of the objective lens 7 and the collimator lens 3 are orthogonal, and the aberration of the optical head is reduced.

  Also in this case, as in the second embodiment, the amount of astigmatism in the optical head can be reduced, but cannot be completely reduced to zero. Therefore, the direction of astigmatism of the objective lens 7 or the collimator lens 3 is matched with the beam shaping direction, and astigmatism is canceled by fine adjustment of the collimator lens. Accordingly, it is possible to suppress the aberration of the optical head in FIG. 6 to be small, and it is possible to improve the condensing characteristic of the objective lens of the optical head.

  In the optical head of FIG. 6, for example, when reproducing a single-layer information recording medium or when a certain amount of spherical aberration is allowed by signal processing, the spherical aberration correcting means may be omitted. Even in this case, an optical head having good condensing characteristics can be configured by the method of the fourth embodiment.

(Embodiment 5)
In Embodiment 5, an example of the optical head of the present invention will be described.

  FIG. 7 is a configuration diagram of an optical head according to the fifth embodiment. The optical head in FIG. 7 is the same as that described in the first embodiment, and a duplicate description is omitted. The optical head in FIG. 7 focuses on the objective lens 7 and the detection lens 15, and reduces the astigmatism of the signal light reflected from the information recording medium 8 and incident on the light detection element 10. The respective lenses are arranged so that the astigmatism directions of the objective lens 7 and the detection lens 15 are orthogonal, and the light beam condensing characteristic of the optical head is improved.

(Embodiment 6)
FIG. 8 illustrates an example in which the optical head of the present invention is applied to an optical information recording / reproducing apparatus for recording and reproducing signals on an information recording medium.

  FIG. 8 schematically shows the configuration of the optical information recording / reproducing apparatus according to the sixth embodiment. The optical information recording / reproducing apparatus includes an optical head 21 of the present invention, a motor 20, a control circuit 19, and a processing circuit 18.

  The light emitted from the optical head 21 is collected on the information recording medium 8. The light reflected from the information recording medium 8 passes through the objective lens 7, is reflected by the beam splitter 4, and is condensed on the light detection element 10 by the detection lens 9. The output from the light detection element 10 is output by the arithmetic processing unit as a focus error signal indicating the focused state of the light on the information recording medium 8 according to the condensed light, and a tracking error indicating the irradiation position of the light. Output a signal. Here, the focus error signal and the tracking error signal are detected by a known technique, for example, by the astigmatism method and the push-pull method.

  A focus control means (not shown) controls the position of the objective lens 7 in the direction of the optical axis so that light is always focused on the information recording medium 8 in a focused state based on the focus error signal. A tracking control means (not shown) controls the position of the objective lens 7 based on the tracking error signal so that the light is condensed on a desired track on the information recording medium 8. Information recorded on the information recording medium 8 is also obtained from the light detection element 10.

  Next, the operation of the optical information recording / reproducing apparatus in FIG. 8 will be described. First, when the information recording medium 8 is set in the optical information recording / reproducing apparatus, the control circuit 19 outputs a signal for rotating the motor 20 to rotate the motor 20. Next, the control circuit 19 drives the light source 2 to emit light. The light emitted from the light source 2 is reflected by the information recording medium 8 and enters the light detection element 10. The light detection element 10 outputs a focus error signal indicating a focused state of light on the information recording medium 8 and a tracking error signal indicating a light irradiation position to the processing circuit 18. Based on these signals, the control circuit 19 outputs a signal for controlling the objective lens 7, thereby condensing the light emitted from the light source 2 onto a desired track on the information recording medium 8. The processing circuit 18 reproduces information recorded on the information recording medium 8 based on a signal output from the light detection element 10.

  The optical head and the optical information recording / reproducing apparatus of the present invention are useful for an optical information recording / reproducing apparatus using an optical disk such as a magneto-optical recording apparatus, a DVD, or a Blu-ray disk apparatus. It can also be applied to optical systems and devices of hologram recording devices and future ultra-high density recording / reproducing devices.

1 is a configuration diagram of an optical head according to a first embodiment of the present invention. Explanatory drawing for defining the direction of astigmatism of an optical element such as a lens in the first embodiment of the present invention. The figure which shows the example which calculated concretely the relationship between the astigmatism of a spherical aberration correction system, and the angle which each astigmatism vector of the said spherical aberration correction system structure lens makes in the 1st Embodiment of this invention. Configuration diagram of an optical head according to a second embodiment of the present invention Configuration diagram of an optical head according to a third embodiment of the present invention The block diagram of the beam shaping optical system concerning the 4th Embodiment of this invention Configuration diagram of an optical head according to a fifth embodiment of the invention The block diagram of the optical information recording and reproducing apparatus concerning the 6th Embodiment of this invention Configuration diagram of an optical head having a conventional beam shaping optical system

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens 2 Light source 3 Collimator lens 4 Beam splitter 4 'Beam shaping optical element 5 1st lens 6 2nd lens 7 Objective lens 8 Information recording medium 9 Detection lens 10 Photodetection element 11 1st mark 12 2nd mark 13 third mark 14 fourth mark 15 fifth mark 16 first actuator 17 second actuator 18 processing circuit 19 control circuit 20 motor 101 light source 102 collimator lens 103 beam splitter 104 first lens 105 second lens Lens 106 Spherical Aberration Correction Unit 107 Objective Lens 108 Information Recording Medium 109 First Actuator 110 Second Actuator 111 Detection Lens 112 Photodetection Element

Claims (25)

An optical head for recording or reproducing a signal with respect to an information recording medium,
A light source;
Spherical aberration correction means for correcting spherical aberration that occurs when the thickness of the recording surface protective layer of the information recording medium deviates from a standard value;
An objective lens for condensing the light emitted from the light source on the information recording medium;
In an optical head comprising a light detection element that receives reflected light from the information recording medium and outputs a signal for reproducing information recorded on the information storage medium.
The spherical aberration correction means is composed of a negative lens and a positive lens,
In the positive lens and the negative lens, the astigmatism directions of the respective lenses are substantially perpendicular to each other. An optical head for recording or reproducing a signal with respect to an information recording medium,
A light source;
Spherical aberration correction means for correcting spherical aberration that occurs when the thickness of the recording surface protective layer of the information recording medium deviates from a standard value;
An objective lens for condensing the light emitted from the light source on the information recording medium;
In an optical head comprising a light detection element that receives reflected light from the information recording medium and outputs a signal for reproducing information recorded on the information storage medium.
The spherical aberration correction means is composed of a negative lens and a positive lens,
In the positive lens and the negative lens, the direction of astigmatism of each lens is substantially orthogonal,
Furthermore, an optical head in which the astigmatism direction of the positive lens or the negative lens is substantially equal to the beam shaping direction of the beam shaping optical element. 3. The optical head according to claim 1, wherein the spherical aberration correcting means further has a chromatic aberration correcting function. The optical head according to any one of claims 1 to 3, wherein the positive lens is a lens group including two or more lenses. The optical head according to any one of claims 1 to 3, wherein the negative lens is a lens group including two or more lenses. 6. The optical head according to claim 4, wherein the positive lens and the negative lens are cemented lenses obtained by cementing two or more lenses made of glass materials having different Abbe numbers. 8. The optical head according to claim 1, wherein at least one surface of the lens surface of the lens constituting the positive lens or the negative lens is an aspheric surface. 9. An optical head for recording or reproducing a signal with respect to an information recording medium,
A light source;
A collimator lens for converting an emitted light beam from the light source into a parallel light beam;
An objective lens for condensing the parallel light flux on the information recording medium;
In an optical head comprising a light detection element that receives reflected light from the information recording medium and outputs a signal for reproducing information recorded on the information storage medium.
An optical head in which the direction of astigmatism of the collimator lens and the direction of astigmatism of the objective lens are substantially orthogonal. An optical head for recording or reproducing a signal with respect to an information recording medium,
A light source;
A collimator lens for converting an emitted light beam from the light source into a parallel light beam;
A beam shaping optical element for converting the light quantity distribution of the parallel light flux into a circle;
An objective lens for condensing the parallel light flux on the information recording medium;
In an optical head comprising a light detection element that receives reflected light from the information recording medium and outputs a signal for reproducing information recorded on the information storage medium.
The direction of astigmatism that the collimator lens has and the direction of astigmatism that the objective lens has are approximately orthogonal,
Further, the direction of astigmatism that the collimator lens has, or the direction of astigmatism that the objective lens has,
An optical head having substantially the same beam shaping direction as the beam shaping optical element. 10. The optical head according to claim 8, wherein the positive collimator lens is a cemented lens in which two or more lenses made of glass materials having different Abbe numbers have a function of correcting chromatic aberration. The optical head according to claim 8, wherein at least one surface of the objective lens or the collimator lens is an aspheric surface. An optical head for recording or reproducing a signal with respect to an information recording medium,
A light source;
An objective lens for condensing the light from the light source onto the information recording medium;
A detection lens for converting the return light reflected by the information storage medium into convergent light;
In an optical head comprising: a light detecting element that receives the convergent light and outputs a signal for reproducing information recorded in the information storage medium;
An optical head in which an astigmatism direction of the objective lens and an astigmatism direction of the detection lens are substantially orthogonal to each other. The optical head according to any one of claims 2 to 7, or 9 to 11, wherein the beam shaping optical element is a prism. The optical head according to any one of claims 2 to 7, or 9 to 11, wherein the beam shaping optical element is a lens. In the positive lens and the negative lens constituting the spherical aberration correction unit,
A mark indicating the direction of astigmatism is applied to an intersection of a straight line passing through each lens central axis and extending in the direction of astigmatism of each lens and the outer periphery of each lens. 8. The optical head according to any one of 7 above. The positive lens and the negative lens are held in a lens barrel,
A mark indicating the direction of astigmatism is applied at the intersection of a straight line that passes through the center axis of each lens and goes in the direction of astigmatism of each lens and the lens barrel holding each lens. The optical head according to claim 1. The mark indicating the direction of astigmatism is applied to an intersection of a straight line that passes through the central axis of the objective lens and extends in the direction of astigmatism of the objective lens and the outer periphery of the objective lens. 14. The optical head according to any one of 14. The objective lens is held in a lens barrel, and at the intersection of a straight line that passes through the central axis of the objective lens and goes in the direction of astigmatism of the objective lens, and the lens barrel that holds the objective lens The optical head according to any one of claims 8 to 14, wherein a mark indicating a direction of astigmatism is applied. 9. A mark indicating the direction of astigmatism is applied to an intersection between a straight line passing through the central axis of the collimator lens and extending in the direction of astigmatism of the collimator lens and the outer periphery of the collimator lens. 11. The optical head according to any one of 11 above. The collimator lens is held in a lens barrel, and intersects a straight line that passes through the central axis of the collimator lens and travels in the direction of astigmatism of the collimator lens, and the lens barrel that holds the collimator lens. The optical head according to any one of claims 8 to 11, wherein a mark indicating a direction of astigmatism is applied. The light according to claim 12, wherein a mark indicating the direction of astigmatism is applied to an intersection of a straight line that passes through the central axis of the detection lens and extends in the direction of astigmatism of the detection lens and the outer periphery of the detection lens. head. The detection lens is held in a lens barrel, and at the intersection of a straight line that passes through the central axis of the detection lens and goes in the direction of astigmatism of the detection lens, and the lens barrel that holds the detection lens The optical head according to claim 12, wherein a mark indicating the direction of astigmatism is applied. The optical head according to claim 1, wherein an NA of the objective lens is 0.7 or more. The optical head according to any one of claims 1 to 23, wherein a wavelength of the light source is not less than 380 nm and not more than 420 nm. An optical information recording / reproducing apparatus for recording or reproducing a signal to / from an information recording medium,
An optical head for recording or reproducing signals on the information recording medium;
The optical information recording / reproducing apparatus according to claim 1, wherein the optical head is an optical head according to claim 1.

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